This invention relates generally to mechanically actuated fuel injection systems, and more particularly to a method of reducing noise in a mechanically actuated fuel injection system.
In engines utilizing mechanically actuated electronically controlled fuel injectors, a tappet included on the mechanically actuated fuel injector is controlled in its movement by the reciprocating motion of a rocker arm in contact with the fuel injector. One example of such a fuel injector is disclosed in U.S. Pat. No. 6,113,014, which issued to Coldren et al. On Sep. 5, 2000. As the rocker arm is moved downward by movement of the rocker arm assembly and lifter arm assembly, a tappet included on the fuel injector is driven downward, causing a plunger included in said fuel injector to pressurize fuel for an injection event. As the rocker arm is moved upward, the tappet is allowed to return to an upward position under the action of a biasing spring, allowing fresh fuel to be drawn into the fuel injector for the next injection event.
In fuel injectors such as these, the timing and duration of the injection event is controlled by an electrically controlled needle control valve member that is movably positioned in the injector body, while timing of fuel pressurization within the fuel injector is controlled by an electrically controlled spill valve member. Prior to initiation of an injection event, the tappet begins its downward movement in response to movement of the rocker arm. When it is time for an injection event to commence, the spill valve member is moved to a position blocking the fuel pressurization chamber from a spill passage. The needle control valve member is then moved to a position blocking a closing hydraulic surface of the direct control needle valve from high pressure fluid, thus relieving pressure on the needle valve member. High pressure acting on an opening hydraulic surface of the needle valve can then reach a sufficient amount to lift the needle and allow fuel spray to begin. At the end of the injection event while the tappet is still being driven toward its downward position, the needle control valve member is moved to a position re-opening the closing hydraulic surface to high pressure fluid and the needle valve is moved to a closed position, blocking fuel spray. The injection event is ended by opening the fuel pressurization chamber to the spill passage, thus causing pressure within the injector body, including that acting on the opening hydraulic surface of the needle valve, to decrease. After the injection event has ended, the tappet continues to be driven to its downward position, and eventually begins to retract toward its upward position under the action of the rocker arm after the peak of the cam lobe is passed.
Because the tappet continues in its downward movement after the spill passage is open, the energy dissipation associated with the high rate of pressure decay can have a strong influence on the movement of various engine components positioned upstream from the tappet. For instance, when the momentum of the tappet toward its downward position is less than the momentum of fuel being forced out of the spill passage, those engine components upstream of the tappet can briefly separate and re-engage, which can result in increased mechanical noise levels. This separation can occur between such components as gear teeth, roller followers and cam lobes. The impacts caused by the separation and re-engaging of the components can also contribute to premature component wear and failure.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a mechanically actuated direct control fuel injection system includes a plurality of mechanically actuated fuel injectors that have an injector body, each of said injector bodies defining a fuel pressurization chamber, a needle control chamber, a fuel inlet and a spill passage. A noise producing linkage couples each of said fuel injectors to an engine. A direct control needle valve is movably positioned in each of the plurality of fuel injectors and includes a closing hydraulic surface that is exposed to fluid pressure in the needle control chamber. A spill valve member is positioned in each of the plurality of fuel injectors and is movable between an open position in which the fuel pressurization chamber is open to the fuel inlet and a closed position in which the fuel pressurization chamber is blocked from the fuel inlet. A flow restriction is positioned in the spill passage and has a flow area that is sufficiently small to reduce noise produced by the noise producing linkage to below a predetermined noise level and sufficiently large to maintain energy losses due to said flow restriction below a predetermined level.
In another aspect of the present invention, an engine including noise reducing features includes a noise producing linkage that is operably coupled to a plurality of mechanically actuated fuel injectors. Each of the fuel injectors provides an injector body that defines a fuel pressurization chamber, a needle control chamber, a fuel inlet and a spill passage. A direct control needle valve is movably positioned in each of the fuel injectors and includes a closing hydraulic surface that is exposed to fluid pressure in the needle control chamber. A low pressure return line fluidly connects the fuel pressurization chamber to a source of fuel, wherein the spill passage is a portion of the low pressure return line. A spill valve member is positioned in each of the fuel injectors and is movable between an open position in which the fuel pressurization chamber is open to the fuel inlet and a closed position in which the fuel pressurization chamber is blocked from the fuel inlet. A flow restriction is positioned in the low pressure return line and has a flow area that is sufficiently small to reduce noise produced by the noise producing linkage to below a predetermined noise level and sufficiently large to maintain energy losses due to the flow restriction to below a predetermined loss level.
In yet another aspect of the present invention, a method of reducing noise in a mechanically actuated fuel injection system includes a step of providing a mechanically actuated fuel injection system that has a plurality of mechanically actuated fuel injectors that each have an injector body that defines a spill passage and a fuel pressurization chamber and includes a direct control needle valve, wherein each of the fuel injectors is coupled to an engine by a noise producing linkage. Noise produced by the noise producing linkage is reduced to below a predetermined noise level at least in part by restricting flow in the spill passage.